The present invention relates to a roller bending apparatus for forming metal stock. More particularly but no exclusively, it relates to a three-roller bending apparatus in which the curvature of the material being rolled can be automatically measured and in which the rolling process can be automatically controlled so as to achieve a finished product having a desired curvature.
Three-roller bending involves imposing a bending moment on a material at the same time that the material is being rolled between two lower rollers and a top roller, the bending moment being applied through the top roller which can be moved up and down by suitable means and the driving force for moving the material being provided by the lower rollers which are driven by motors. Generally, control of the shape of the material is performed manually. Namely, after each stage of rolling, an operator compares the shape of the material being rolled with a template and then adjusts the position of the top roller accordingly, relying largely on his experience and on intuition. This method is time-consuming and inaccurate, being subject to error on the part of the operator. In addition it requires the manufacture of a large number of templates, since different templates are necessary every time a workpiece having a different curvature is to be rolled.
Furthermore, a highly trained operator is necessary to adjust the setting of the top roller based on the measured shape of the material because it is very difficult to predict the relationship between a given roller position and the resulting shape of the material after rolling.
A different problem encountered in three-roller bending is that a gap may develop between the top roller and the material being rolled due to the fact that the end portions of a material being rolled remain straight during rolling. Since the bottom rollers can not transport the material unless the top roller presses the material from above, such a gap makes it impossible for the material to be moved and rolling can not take place. The top roller must then be further lowered until it contacts the workpiece, but by further lowering of the top roller, the workpiece may end up being overbent and therefore unusable.